1. Field of the Invention
This invention relates to compositions that are useful as ink jet recording media topcoats, recording media for ink jet images, processes for making ink jet recording media, processes for recording images on ink jet recording media and images made by such processes.
2. Description of Related Art
Ink jet printers are a well known means for creating black and white and color images on a recording medium. The images are created by generating small droplets of ink which are propelled onto the recording medium. The ink generally contains a water-based dye or dispersed pigment and the recording medium is often paper, but may also be a coated polymeric film as in the case of transparencies for overhead projectors. Advantages with this type of printing include the ability to create high resolution full color images rapidly and in large formats using digitally generated and stored images. It is quiet and environmentally friendly and safe.
However, the prior art has had to deal with certain disadvantages in using conventional ink jet printers. The ink had to be absorbed as quickly as possible by the recording medium in order to allow the recording medium to be handled soon after the ink has been applied and yet the ink has to be prevented from diffusing or spreading too far through and into the recording medium. That disadvantage becomes acute when attempting to obtain photographic quality resolution.
A further disadvantage of the prior art methods of ink jet recording is that the image lacked water and abrasion resistance. These two defects, along with the lack of lightfastness of dyes commonly used in ink jet inks, have hindered the application of ink jet printing to products which require outdoor weatherability.
The lightfastness problem may be combated by printing with pigmented inks that contain fine dispersions of highly UV-resistant pigments. The most common method used in the industry to impart waterfastness is the application of overlaminates. This significantly increases the cost of the product, the process can be quite awkward, and delamination or pick-off from the base film may occur, especially when the print is applied to a non-planar surface such as the riveted side panels of a truck in the case of fleet graphics.
One reason for the lack of water-resistance of the prior art ink jet recording media is that most of the coatings applied to polymeric film are based upon water-soluble polymers such as poly(vinyl alcohol). Several of these water-soluble polymers may be crosslinked, but the absorptivity of the coatings suffers if the degree of crosslinking is too great. Even when crosslinked, these highly hydrophilic polymers are still swelled somewhat by water. For an indoor application like an overhead transparency where smudge resistance upon handling is the main issue, the swelling of the coating does not present a major problem. However, for outdoor applications exposure of a swellable coating to rain will result in fading due to liberation of the colorant and will likely also eventually cause the removal of the coating from the underlying polymeric film.
The lack of outdoor weatherability and other disadvantages observed in the prior art are overcome by this invention.